Heat-sealable coating consisting of polyvinyl alcohol, urea, and dextrose



United States Patent HEAT-SEALABLE COATING CONSISTING OF POESSIVINYLALCOHOL, UREA, AND DEX- TR E Norman Bruce Oakley, Hopewell, Va.,assignor to Hercules Powder Company, Wilmington, Del., a corporation ofDelaware No Drawing. Application April 11, 1952, Serial No. 281,888

12 Claims. (Cl. 260-1744) This invention relates to the art of packagingmaterials. In a specific aspect this invention relates to a novelheatsealing coating composition and to the method of heatsealingpackaging films with said composition. In a more specific aspect thisinvention relates to novel watersoluble, heat-sealing coatingcompositions and to the method of heat-sealing water-soluble films ofcellulose derivatives with said compositions.

Throughout this specification polyvinyl alcohol (PVA) refers to a groupof closely related compounds made by the saponification or hydrolysis ofpolyvinyl esters, particularly polyvinyl acetate. The resulting productsare either water-soluble or water-insoluble depending in part on theextent to which the product is saponified or hydrolyzed. Althougheifective heat-sealing coating compositions can be prepared with thewater-insoluble products, such as a 47% hydrolyzed polyvinyl acetate ofhigh viscosity, it is preferred for this invention that the polyvinylacetate be sufiiciently hydrolyzed to produce a substantiallywater-soluble polyvinyl alcohol.

In the packaging field, heat-sealing coatings are employed ratherextensively in the sealing of the packages or films. Among therequirements for an effective heatsealing composition are that thecomposition be compatible with the film or packaging material and thatthe composition be effective for producing a strong seal. It is anobject of this invention to provide novel and elfective heat-sealingcompositions for use in the packaging art.

Cellulose derivatives, either water-soluble or waterinsoluble, are usedfor the formation of packaging films or pellicles. Among thewater-insoluble cellulose derivatives that can be used are cellophaneand the like, and among the water-soluble cellulose derivatives that canbe used are carboxymethyl hydroxyethyl cellulose, carboxymethylcellulose, methyl cellulose, hydroxyethyl cellulose, cellulose sulfate,and the like. In my copending application, Serial No. 203,529, filedDecember 29, 1950, now U. S. Patent 2,653,108, a packaging filmcontaining carboxymethyl hydroxyethyl cellulose is described. It isanother object of this invention to provide novel heat-sealingcompositions for the sealing of packaging films of cellulosederivatives.

Water-soluble cellulose derivatives, such as carboxymethyl hydroxyethylcellulose, and the like, have been found to be quite elfective for thepackaging of comestibles and materials, such as detergents, soappowders, and the like. In the packaging of such materials withwatersoluble cellulose derivatives as the packaging film or pellicle, itis desirable that the composition that is employed to seal the film orpellicle be water-soluble in ice order that the entire film can bedissolved in water. It is another object of this invention to providenovel and efiective water-soluble heat-sealing coating compositions forsealing films or pellicles of water-soluble cellulose 5 derivatives.

It is another object of this invention to provide novel and efiectiveheat-sealing coating compositions for sealing water-soluble films orpellicles of carboxymethyl hydroxyethyl cellulose.

It is a further object of this invention to provide novel and efiectiveheat-sealing coating compositions for the sealing of water-soluble filmsor pellicles comprising carboxymethyl hydroxyethyl cellulose,dipropylene glycol, and glycerin.

It is a still further object of this invention to provide a novel methodof heat-sealing packaging films or pellicles employing novel coatingcompositions for said films or pellicles.

Further and additional objects of this invention will be readilyapparent from the detailed disclosure that follows.

In accordance with this invention it has been found that compositionscontaining polyvinyl alcohol in a concentration of at least 50% and atleast one of urea and dextrose are eifective heat-sealing coatingcompositions for packaging films or pellicles. In the preferred form ofthe invention, the heat-sealing composition contains both urea anddextrose in addition to the polyvinyl alcohol. This discovery isparticularly astounding in view of the fact that polyvinyl alcohol,although it possesses heat-sealing properties, is poorly compatible withvarious cellulose derivatives and tends to form laminar coatings whenemployed in a heat-sealing composition. Urea, on the other hand, hasbeen found to be inefiective as a heat-sealing coating composition.

The following examples are illustrative of this invention. In thecoating formulations for each of the runs, the compositions of thecoatings are in parts by weight.

Examples 1-9 In the following runs, a film containing 65 parts ofcarboxymethyl hydroxyethyl cellulose, 25 parts of dipropylene glycol and10 parts of glycerin was coated with the coating formulations indicatedbelow, and the film was then heat-sealed with a hand model Power Weldsealer at a surface temperature of 240 F. The. polyvinyl alcohol (PVA)was 77% hydrolyzed polyvinyl acetate of medium viscosity. The bondstrengths were measured by clamping a weight to pull apart a seal 0.5inch deep by 1 inch wide, applying the tension at distances 0.5 inch oneach side of the seal.

Coating Formulation Bond Strength Poor.

Do. Good. Fair.

Do. Good. Fair.

PVA/urea80/2O Examples 10-27 Coating formulations of the compositionslisted below were employed to heat-seal a film as in Example 1. The

bond strength of the film was observed in grams per inch.

Coating Formulation PVA Examples 28-33 In addition to the water-solublefilms containing carboxymethyl hydroxyethyl cellulose described above, acoating containing 90 parts PVA, parts urea and 5 parts dextrose wasemployed to heat-seal the following water-soluble films:

1. 80 parts carboxymethyl hydroxyethyl cellulose and 20 partsdipropylene glycol;

2. Sodium carboxymethylcellulose having a .70 degree of substitution;

3. 80 parts sodium carboxymethylcellulose having a .70 degree ofsubstitution and 20 parts glycerin;

4. 80 parts methyl cellulose having a viscosity of 25 cps. and 20 partsglycerin;

5. 80 parts sodium cellulose sulfate of low viscosity and having a .4degree of substitution and 20 parts glycerin;

6. 80 parts hydroxyethyl cellulose having a 1.4 degree of substitutionand 20 parts glycerin.

Example 34 The same coating formulation used in Examples 28-33 was alsoemployed to effectively seal a water-insoluble film of cellophane.

The polyvinyl alcohol, urea and dextrose that are employed to form theheat-sealing coatings of this invention are available commercially.Although water-insoluble forms of polyvinyl alcohol can be used inheat-sealing packaging films, it is preferred to employ a polyvinylalcohol that has been sufficiently hydrolyzed to substantial watersolubility in order that the heat-sealing composition wil bewater-soluble. Consequently, the composition can be employed effectivelywith water-soluble films. Although polyvinyl alcohol can be employedalone as a heat-sealing composition, it has disadvantages in that it isincompatible with certain films, such as those containing carboxymethylhydroxyethyl cellulose, and as a coating it tends toward lamination.Accordingly, improved heat-sealing coatings can be obtained byincorporating urea and/or dextrose in the polyvinyl alcohol. Thepresence of the urea in the composition improves the adhesion of thecoating, and it also lowers the fusion temperature of the polyvinylalcohol. The data in Examples -27 above indicate that in order to obtaina seal with a coating composition containing polyvinyl alcohol, thecomposition should contain a minimum of 50 parts by weight of polyvinylalcohol based on 100 parts of coating composition. The remaining portionof the composition is composed of urea and/or dextrose in variousproportions. In a preferred form of the invention, the coatingcomposition contains about 90 parts of polyvinyl alcohol per 100 partsof composition. The remaining portion of the composition is urea and/ordextrose. The presence of the urea is desired in order to improve theadhesion of the coating, and eifective heat unplasticized) Bond Strengthseals have been obtained with a coating composition containing parts ofpolyvinyl alcohol and 10 parts of urea. However, it was found that whena film heatsealed with such a composition was exposed to a high humidityor to an average humidity for an extended period of time, the coatingcomposition lost its bond strength. The presence of the dextrose in thecoating composition overcomes this defect. Accordingly, the mostpreferred coating composition of this invention contains 90 partspolyvinyl alcohol, 5 parts urea and 5 parts dextrose. It will beunderstood by those skilled in the art that numerous other combinationsof these three components can be employed provided the composition doesnot contain less than 50 parts of polyvinyl alcohol per parts of coatingcomposition.

From the above examples, it is apparent that the coating composition ofthis invention can be employed in the heat-sealing of bothWater-insoluble and water-soluble films. In the preferred form of theinvention, the coating composition is water-soluble, and it is employedin the heat-sealing of films made of water-soluble cellulosederivatives. In the most preferred form of the invention, the coatingcomposition is employed in the heatsealing of films containingcarboxymethyl hydroxyethyl cellulose, such as the films describedparticularly in Examples 1-9. The carboxymethyl hydroxyethyl cellulosecontains a degree of substitution such that the cellulose derivative iswater-soluble. The degrees of substitution that were employed in theabove examples are 0.43 carboxymethyl and 0.35 hydroxyethyl substituentsper anhydroglucose unit. However, it will be understood that otherdegrees of substitution can be used without departing from the scope ofthe invention.

The coating composition can be applied to the film to be sealed in anysuitable manner. In most instances, the composition will be dissolved ina solvent and then applied to the film. In the above examples, thecoating composition was applied in this manner. Any solvent that willimpart the necessary viscosity to the solution and that is not a solventfor the film to be sealed can be used. Effective solvents are the loweraliphatic alcohols, such as methanol, ethanol, and the like. In theabove examples, a 1:1 ethanol/water solvent was employed. The loweraliphatic alcohols appear to be the most practical solvents for theapplication of polyvinyl alcohol coating compositions to packagingfilms. Sufficient solvent is used to obtain a solution containing nomore than about 20% solids in order to insure a thin heat-sealingcoating. Preferably a solution containing from 5% to 10% solids is usedto insure a thin coating of about 0.1 to 0.2 mil in thickness.

The heat-sealing composition can be applied to the film to be sealed inany suitable manner. For example, the solution containing the coatingcomposition can be sprayed, brushed, rolled or otherwise applied to thefilm. Any satisfactory method of application is within the scope of theinvention, and after application the film is heatsealed at a temperaturewithin the range of F. to 350 F. In the above examples, a temperature of240 F. was found to be satisfactory.

Packaging films sealed in accordance with this invention can be used topackage detergents, foodstuffs, household and industrial dyes, starch,insecticides, Weed-killers, water softeners, and the like.

Numerous modifications within the scope of this invention will beapparent to those skilled in the art.

What I claim and desire to protect by Letters Patent is:

l. A water-soluble envelope comprising a packaging film of awater-soluble film forming cellulose derivative and a water-soluble,heat-sealable coating consisting essentially of polyvinyl alcohol, ureaand dextrose, said polyvinyl alcohol being present in said coating in anamount at least equal to 50 parts by weight per 100 parts by weight ofcoating, said urea and dextrose each being present in said coating in anamount at least equal to 2 parts by weight per 100 parts by weight ofcoating, the sum of the amounts of said urea and dextrose present insaid coating not exceeling 50 parts by weight per 100 parts by weight ofcoating.

2. A Water-soluble envelope comprising a packaging film of water-solublecarboxymethyl hydroxyethyl cellulose and a water soluble, heat-scalablecoating consisting essentially of polyvinyl alcohol, urea and dextrose,said polyvinyl alcohol being present in said coating in an amount atleast equal to 50 parts by weight per 100 parts by weight of coating,said urea and dextrose each being present in said coating in an amountat least equal to 2 parts by weight per 100 parts by weight of coating,the sum of the amounts of said urea and dextrose present in said coatingnot exceeding 50 parts by weight per 100 parts by weight of coating.

3. A water-soluble envelope comprising a packaging film of Water-solublesodium carboxymethylcellulose and a water-soluble, heat-scalable coatingconsisting essentially of polyvinyl alcohol, urea and dextrose, saidpolyvinyl alcohol being present in said coating in an amount at leastequal to 50 parts by weight per 100 parts by Weight of coating, saidurea and dextrose each being present in said coating in an amount atleast equal to 2 parts by weight per 100 parts by weight of coating, thesum of the amounts of said urea and dextrose present in said coating notexceeding 50 parts by weight per 100 parts by weight of coating.

4. A water-soluble envelope comprising a packaging film of water-solublehydroxyethyl cellulose and a watersoluble, heat-sealable coatingconsisting essentially of polyvinyl alcohol, urea and dextrose, saidpolyvinyl alcohol being present in said coating in an amount at leastequal to 50 parts by weight per 100 parts by weight of coating, saidurea and dextrose each being present in said coating in an amount atleast equal to 2 parts by weight per 100 parts by weight of coating, thesum of the amounts of said urea and dextrose present in said coating notexceeding 50 parts by weight per 100 parts by weight of coating.

5. A water-soluble envelope comprising a packaging film of water-solublemethyl cellulose and a water-soluble, heat-scalable coating consistingessentially of polyvinyl alcohol, urea and dextrose, said polyvinylalcohol being present in said coating in an amount at least equal to 50parts by weight per 100 parts by weight of coating, said urea anddextrose each being present in said coating in an amount at least equalto 2 parts by weight per 100 parts by weight of coating, the sum of theamounts of said urea and dextrose present in said coating not exceeding50 parts by weight per 100 parts by Weight of coating.

6. A water-soluble envelope comprising a packaging film of water-solublecellulose sulfate and a water-soluble, heat-scalable coating consistingessentially of polyvinyl acohol, urea and dextrose, said polyvinylalcohol being present in said coating in an amount at least equal to 50parts by weight per 100 parts by weight of coating, said urea anddextrose each being present in said coating in an amount at least equalto 2 parts by weight per 100 parts by weight of coating, the sum of theamounts of said urea and dextrose present in said coating not exceeding50 parts by weight per 100 parts by weight of coating.

7. A water-soluble envelope comprising a packaging film of carboxymethylhydroxyethyl cellulose containing 0.43 carboxymethyl and 0.35hydroxyethyl substituents per anhydroglucose unit, d'ipropylene glycoland glycerin and a heat-sealable coating consisting essentially ofpolyvinyl alcohol, urea and dextrose, said polyvinyl alcohol beingpresent in said coating in an amount at least equal to 50 parts byweight per 100 parts by weight of coating, said urea and dextrose eachbeing present in said coating in an amount at least equal to 2 parts byweight per 100 parts by weight of coating, the sum of the amounts ofsaid urea and dextrose present in said coating not exceeding 50 parts byweight per 100 parts by weight of coating.

8. An envelope according to claim 7 wherein the coating contains partspolyvinyl alcohol, 5 parts urea and 5 parts dextrose.

9. As a composition of matter, a heat-sealing coating compositionconsisting essentially of a lower aliphatic alcohol solution containingas solute 90 parts by weight of polyvinyl alcohol, 5 parts by weighturea and 5 parts by weight dextrose, based on the weight of the solute.

10. As a composition of matter, a heat-scalable coating compositionconsisting essentially of an ethanol solution containing as solute 90parts by Weight of watersoluble polyvinyl alcohol, 5 parts by weighturea and 5 parts by weight dextrose.

1 1. As a composition of matter, a heat-scalable coating compositionconsisting essentially of an ethanol solution containing as solute 90parts by weight of watersoluble polyvinyl alcohol, 5 parts by weighturea and 5 parts by weight dextrose, said solution having a solidscontent not greater than 20% 12. As a composition of matter, aheat-scalable coating composition consisting essentially of a loweraliphatic alcohol solution containing as solute at least 50 parts byweight of water-soluble polyvinyl alcohol and not more than 50 parts byWeight of urea and dextrose, said urea and dextrose each being presentin the composition in an amount at least equal to 2 parts by Weight.

References Cited in the file of this patent UNITED STATES PATENTS2,162,618 Izard June 13, 1939 2,275,578 Wood Mar. '10, 1942 2,298,522Waters Oct. I13, 1942 2,340,311 Donovan Feb. 1, 1944 2,340,866Dangelmajer Feb. 8, 1944 2,349,732 Howard May 23, 1944 2,373,285 BaerApr. 10, .1945 2,432,575 King Dec. I16, 1947 2,457,357 Penn Dec. 28,1948 2,579,481 Fenn Dec. 25, 1951 2,579,483 Fenn Dec. 25, 1951 2,595,276Lowry May 6, 1952 2,653,108 Oakley Sept. 22, 1953

1. A WATER-SOLUBLE ENVELOPE COMPRISING A PACKAGING FILM OF AWATER-SOLUBLE FILM FORMING CELLULOSE DERIVATIVE AND A WATER-SOLUBLE,HEAT-SEALABLE COATING CONSISTING ESSENTIALLY OF POLYVINYL ALCOHOL, UREAAND EXTROSE, SAID POLYVINYL ALCOHOL BEING PRESENT IN SAID COATING IN ANAMOUNT AT LEAST EQUAL TO 50 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OFCOATING, SAID UREA AND DEXTROSE EACH BEING PRESENT IN SAID COATING IN ANAMOUNT AT LEAST EQUAL TO 2 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OFCOATING, THE SUM OF THE AMOUNTS OF SAID UREA AND DEXTROSE PRESENT INSAID COATING NOT EXCEEDING 50 PARTS BY WEIGHT PER 100 PARTS BY WEIGHT OFCOATING.